Pressure-controlled electric switch



A. B- COBB.

PRESSURE CONTROLLED ELECTRIC SWITCH. APPLICATION FILEDIULY161191B. 1,377,317. Patented May 10,1921,

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UNITED STATES PATENT OFFICE.

ALBERT B. COBB, 0F BOSTON, MASSACHUSETTS, ASSIGNOR To COBB ELECTRIC APPLI- ANGE 00., or BOSTON, MASSACHUSETTS, A CORPORATION or MAssACnUsE PRESSURE-CONTROLLED ELECTRIC SWITCLI.

' Application filed July 16, 1918.

T 0 all 'ltllQ/H it may concern Be it known that I, ALBERT B. Conn, a. citizen of the United States, residing at Boston, in the county of Suffolk and State of Massachusetts, have invented new and useful Improvements in Pressure-Controlled Electric Switches, of which the following is a specification.

The object of the present invention is to provide an electric switch adapted to control a circuit containing an electric heating element, and to be controlled in turn by fluid pressures produced or generated in a liquid medium by heat developed and communicated to such liquid medium from the heating element. As further illustrating the character and purpose of the invention I may say that it is intendedfor such purposes as to maintain liquid or vapor at a substantially uniform temperature, as required in various industrial arts. For example, in vulcanizing rubber steam is generally employed as the heating agent, and is maintained for long periods at as nearly uniform temperature as possible. For other purposes where a less degree of heat is required, a heated water bath maintained at substantially uniform temperature is used, as in the manufacture of celluloid and other plastic materials, for maintaining chocolate in fluid condition in the manufacture of confectionery, and for numerous other uses of more or less numerous character. My fundamental purpose is to provide an instrument of the character already indicated which may be adapted without essential change, and generally without greater change than the shifting of an adjustable member, to control the temperature of heating baths and agents in conditions and for usesin which respectively very widely different temperatures are needed; or at most without any change in principle, or other difference than embodiment of the same principles in instruments designed respectively for most efficient operation by specifically different pressures.

My more specific objects,-contributory to the general object above stated, are to combine with an instrument in the nature of a,

pressure gage, a switch'device which is ad j ustab'le for operation at different pressures; and also to'furnish a switch device adapted to be applied without change,except possibly in dimensions, to pressure gages of Specification of Letters Patent.

Patented May 10, 1921.

Serial No. 245,258.

specifically different character. These obects involve the further one of providing a swltch which will be efficiently operative in different positions of adjustment for different pressures, and without change in the mechanical resistance which it opposes to being opened in any of 1ts adjustments.

The precise character of the invention can best be explained by referenceto a specific embodiment thereof and to a detailed description of such embodiment. Accordingly I have shown in complete detail in the drawings which form part of this specification a form of pressure-controlled switch embodying a pressure gage and a switch the instrument on which there is mounted a removable ring 7 for retaining in place the indicating dial 8 and a glass plate which overlies and protects the dial and the pointer 9. A socket 10 passes through the side of the case and is formed on its outer end with provision for attachment to a pipe adapted to contain fluid under pressure, and inside the case it is connected to a curved sprin tube 11 of flattened cross section constltuting the well known Bourdon spring tube of one familiar type of pressure gage. This spring tube receives fluid under pressure and is adapted to be distorted more or less under different pressure conditions, its free end 11 then moving in a path more or less nearly concentric with'the adjacent wall of the case. To this free end 11 is rigidly connected an arm 12 which is piv- Fig. 5 is an elevation fastened by any desired means a block 35 of the case by screws 22,'and 23 represents a bridge secured to the plate 21, said plate and bridge forming a frame in which are mounted the staff 19 and the pivot 24 of the segment. he part of the instrument thus far described is a common pressure gage. The parts about to be described constitute a novel switch in which, and in the combination of which with the elements of the gage, my'invention resides.

A holder 25 is pivoted on a post 26 which is secured to the back of the case 6 and has an extension 26 passing through such back. Preferably the holder is a bar or strip of copper or other electrically conductive metal having one end curved to form a sleeve 25 which surrounds a part of the post 26 and rests on a shoulder thereof, as shown best in Fig. 4. Said sleeve portion is confined by a washer 27 and a holding screw 28 tapped into the post. 29 is a. conductor connected to the'sleeve 25 and to the post 26, conveniently by being soldered to the screw 28, although it may be otherwise connected, for the purpose of establishing a path of low resistance for the flow of electric current between the post and the holder. Said post is insulated from the case of the instrument by a washer 30 of insulating material against which a shoulder 26 on the post bears, inside and against the back of the case, and by an external washer 31 against which a lock nut 32 threaded on the extension 26 bears. 33 is a binding nut adapted to secure a wire, forming part of an electric circuit, to'the post, whereby to put such wire into electrical connection with the holder 25 and with a switch contact 34 on said holder.

On the holder is mounted and securedly insulating material, to which are secured a spring strip 36 and a reinforcing spring 37 by a set screw 38 which is tapped into the block 35 but does not make contact with the holder 25. The spring. strip 36 is of an electrically conductive metal having suflicient stiffness and resilience for the purpose about to be described. I have found that silver is the best material of which to make this part. A switch contact 39 complemental to the contact 34 is carried by the spring strip 36 and normally held by the resilience of the latter against contact 34. These contacts form the essential elements of a switch, and are the only parts of the switch in electrical connection with One another, since the insulating block 35 separates the strip 36 from the holder 25. Contact 39 is, however, connected with another part of the electrical circuit in which the contact 34 is connected,

mounted, and carrying a binding nut 42 for connecting thereto a. wire in the circuit to be ment;

The switch is normally closed, but it may" be opened by the agency of the pressure controlled member of the instrument, that is, the Bourdon spring tube 11. For this purpose said member or tube is provided with a rod or wire 4-tgsecured at one end to the free end 11 of thespri ng tube, and substantially hook shaped atitsother end to engage with a finger 45, which projects outward from the spring piece 36. The hook part is covered by an insulating sleeve or jacket at the point which engages the finger Evidently when the hook is moved by distortion of the spring tube 11 under increase in pressure, the piece 36 is flexed and contact 39 is removed from the complemental contact 34 whereby the circuit is broken. hen the pressure becomes less, motion of the spring tube and of the switch contact 39 takes place in the opposite direction and the switch is closed.

One of the essential features of the invention is provision for adjusting the switch so that it will be opened and closed under different predetermined conditions of pressure or temperature of the fluid which is heated by the heating element thus controlled. For the purpose of thus adjusting the switch I provide a screw 47 which bears against the carrier or holder 25, and a spring 48 which constantly presses the holder yieldingly against said screw with a force materially greater than the spring tension in the piece 36 which resists opening of the switch. The screw is threaded into and through a tapped hole in an anchor block 49 which is secured to the case by a screw 50 but is insulated by tions and maintained therein, to cause open-.

ing and closing when the heated controlling fluid is at any predetermined temperature. The spring-48 is so much more powerful than the spring strip 36, that when the latter is moved by the pressure-operated element 11, the holder '25 is not moved at all.

F or the purposes of this description and of the definition of the invention in the claims, the holder or carrier 25 may be constrip 36 as a secondary holder. Each of these holders carries one of the contacts,

and the secondary holder is so mounted on the primary holder that it permits movement of the separable contact in a prescribed path against yielding resistance away from the contact which is fixed upon the primary holder. By virtue of' the connection between these holders, both are adjusted in unison by the same adjusting means, and in such adjustment the complemental contacts both move in the same path. Thereby the relation between the contacts is not changed in any manner. The contacts are provided with flat faces and are set up in the first place so that their complemental faces bear upon one another as nearly as possible at all points in such faces, in order that when the switch is closed there may be the least possible resistance to flow of current from one contact to the other, and that when the switch is opened the separable contact will withdraw bodily and at all points at the same time from the fixed contact. It is true that the bending of the secondary holder at this time causesthe separable contact to be slightly inclined with respect to the other contact after separation therefrom, but this inclination is inappreciable within the range of movement during which the circuit is broken, wherefore it is true to say that all points of the separable contact are withdrawn simultaneously and equally from the fixed contact 7 at the instant of breaking the circuit; from tion of current equal angles.- 1

all adjusted which it follows that there is'no concentraat-a single point or limited area of the contacts when the switch commences to open, such as would cause generation of extreme tacts together. And this relation holds in positions of the switch, since, when being adjusted, both contacts are shifted about the same pivot point through Another feature of the first importance is that by reason of the mounting of the secondary holder on the primary holder,'the spring resistance of the former is notaltered trivances where the separable contact is pressed upon by a spring which reacts against a fixed abutment, or one which is not adjustable in unison with the other C011, tact, adjustments of the switch cause the tension of such spring to be varied, whereby an error is introduced into" the operation of the instrument, particularly in those wherein-the pressure-measuring element is extremely sensitive, since theforce of the spring acting on the separable contact must be overcome by the said element before the switch can be opened. By reason of the fact that in this in trument the yielding heat and fusing of the con- In conresistance to opening of the switch remains the same in any ad ustment however great, it follows that the switch may be adjusted with reference to the position of the pointer 0n the indicating dial without need of reliance upon some additional instrument.

A means for establishing a short circuit to cause interruption of the heating circuit, by blowing of a fuse or operating a circuit breaker, in case the contacts should become accidentally fused together and fail to separate at the time the switch should be opened, is provided by the finger 45 previously mentioned in cooperation with a pin 53 which is mounted upon the case in a similar manner to posts 26 and 41 previously described. The post 54 from which pin 53 rises is connected in the circuit in such a way that when finger 45 contacts with it a shunt circuit of less resistance than that containing the heating element is completed. The finger is made of metal, preferably annealed copper of such diameter that its stiffness is intermediate that of the secondary holder 36 and that of the spring 18. Thus when the contacts are freely separable, force applied to the finger flexes the secondary holder and removes the separable contact, but when the contacts a e fused together the force capable of being a fialied by the finger will bend the fin 'er into contact with pin 53.

fiy reason of the wide latitude for adjustment permitted by this invention as previously described, the switchmay be made to open and close at any desired point Within the entire range of the pressure measuring movement of the memberflll; that is, if the gage measures pressures from zero to one hundred pounds, the switch may be set to open at any pressure, between a fraction of one pound and one hundred pounds; and correspondingly in gages built for measuring specifically different pressures, adjustments may be made throughout'the entire range of the gage. Or if the indicating part of the instrument is calibrated to read in terms of temperatures instead of pressures, the switch may be set to operate when tihe temperature has risen to any given lthough the instrument here illustrated and shown in Fig. 1 is provided to read in terms of moderate temperatures, this fact is not to be construed as a limitation of the invention, since evidently same whether embodied in an instrument reading in terms of pressures or of temperatures, and whether he temperatures or pressures indicated are high or low. When the temperatures indicated are below the 125 boiling point of water, as .in the case of the instrument here illustrated, a tube or chamber containing a'liquid of low boiling point, or a gas, is connected to the socket of the the invention is the other liquid which is to be heated and maintained at a given temperature.

Vhat I claim and desire to secure by Letters Patent is:

1. In a pressure operated switch, a switch unit comprising a relatively rigid arm having a hub or eye at one end adapted to be mounted upon a pivot, a flexible and resilient strip rigidly secured .to said arm near said hub or eye and being both insulated from the arm and separated therefrom by a space, and complemental contact members mounted upon said arm and flexible strip, respectively, at a distance from the connection between said arm and strip, whereby resilient movement of the arm is effective to cause separation and engagement of the contact members, the pivotal mounting of said arm-enabling both contacts to be adjusted as to osition in unison.

2. pressure operated switch comprising the combination of a pivot, an arm mounted rotatably upon said pivot, an adjusting member bearing against said arm and operable to shift the same, yielding means holding said arms against the adjusting member, a flexible and resilient strip rigidly secured to said arm and insulated and mechanically separated therefrom, and complemental switch contact members carriedvby said arm and strip, respectively, at a distance from the point of connection between the latter, whereby displacement of the flexible strip permitted by its yielding quality causes, respectively, separation and engagement of the contact members, the operation of said adjusting member being effective to adjust both contact members in unison.

3. A pressure operated switch comprising the combination of a pivot, an arm mounted rotatably upon said pivot, an adjusting member bearing against said arm and operable to shift the same, yielding means holding said arm against the adjusting member, a flexible and resilient strip rigidly secured to said arm and insulated and mechanically separated therefrom, and complemental switch contact members carried by said arm and strip, respectively, at a distance from the point of connection between the latter, whereby displacement of the flexible strip permitted by its yielding quality causes, respectively, separation and engagement of the contact members, the operation of said adjusting member being effective to adjust both contact members in unison, a pressure operated means, and connections between said means and the aforesaid flexible strip arranged and operative to cause movement of the strip for the purpose set forth with distortion movement of said pressure operated means.

4. A pressure operated switch comprising the combination of a pivot, an arm mounted rotatably upon said pivot, an adjusting member bearing against said arm and operable t9 shift the same, yielding means holding said arm against the adjusting member, a flexible and resilient strip rigidly secured to said arm and insulated and mechanically separated therefrom, and complemental switch contact members carried by said arm and strip, respectively, at a dis tance from the point of connection between the latter, whereby displacement of the flexible strip permitted by its yielding quality causes, respectively, separation and engagement of the contact members, the operation of said adjusting member being effective to adjust both contact members in unison, a

curved Bourdon spring tube mounted adthe complemental contact member when the spring tube'is distorted by rising internal pressures.

In testimony whereof I have affixed my signature,

ALBERT B. COBB. 

